This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Phosphorylation is one of the most frequent posttranslational modifications of proteins. In a cell, about 30% of the total proteins are phosphorylated to some extent. Protein phosphorlyation-dephosphorylation events play a primary role in almost all aspects of cell function including signal transduction, cell cycle or apoptosis. The activation of the immune response mediated by T lymphocytes is dependent on protein phosphorylation-dephosphorylation events. In order to understand the functionality of lymphocytes in an immune response we need to study the phosphorylation profiles that occur in these cells in response to activation. Considering the complexity of a whole cell lysate and the low amount of phosphorylated peptides versus the non-phosphorylated ones, a robust and effective method for the analysis of the phosphoproteome is of the highest importance in the field of proteomics. Mass spectrometry will be used to identify different posttranslational modifications, such as phosphorylation and their site assignment in human primary T cells. Quantitative methods, such as iTRAQ, will be used to determine the dynamics of the phosphorylation state.